This invention relates generally to a protective device or assembly for electrical current-carrying circuits and more particularly to a fail-safe assembly for the coacting contacts in electrical current-carrying systems, apparatus and electrical and electronic components and devices in which the fail-safe assembly includes an impact member or assembly, held in a stressed, inactive and disengaged position by a meltable material which melts as a function of the condition against which the fail-safe assembly is being used to safeguard and protect the system, apparatus, component or device. When the material melts or fuses, the stress forces of the impact member or assembly will act to impact either directly or indirectly the coacting contacts to move them to the open position and maintain them open.
The impact member or assembly is made of suitable materials and will be sized and shaped to produce the necessary impact forces to insure that the coacting contacts will open and remain open.
In electrical current-carrying circuits, electrical systems, electrical apparatus, electrical and electronic components and associated apparatus, the current flow therethrough is often controlled by coacting contacts, generally one fixed contact and at least one movable contact on a current-carrying movable arm, support or assembly which, when actuated, moves the movable contact into engagement with the fixed contact. The current-carrying movable arm, support or assembly is actuated as a function, for example, of the changes in ambient temperature, the temperature of the movable member or the current load in the system. While this general type of coacting contacts has been described, it will be clear that the present invention is equally applicable where both contacts are movable relative to each other.
Where there are coacting contacts in electrical current-carrying systems, apparatus, components and devices, dangerous conditions often arise, due to current overload or an unacceptable or generated rise in internal or external ambient temperature conditions, causing potentially fire or damage to the component, device, system or associated apparatus. Therefore, it is necessary to effectively guard against the danger of such fire and damage to the electrical or electronic component or device and the electrical system or apparatus in or with which the component is associated.
It is known in the prior art that certain thermal switches and circuit breakers include meltable or fusible assemblies or materials, as fail-safe or safeguard devices, serially connected in associated electrical current-carrying circuits or apparatus to prevent fire or damage. Such devices are shown in U.S. Pat. Nos. 3,611,235; 4,295,114; 4,360,725; 4,313,047; 4,400,677; 4,472,705; 4,885,560 and 4,876,523.
The device shown in U.S. Pat. No. 4,360,725 illustrates a temperature protector for an electrically heated appliance in which a torsion spring has a torsion arm normally held in a stressed position. Such torsion arm is operatively associated with a fusible restraining pin disposed with respect to the movable arm of a switch in the electrical circuit so that upon melting of the fusible pin, the torsion arm moves, thereby releasing the movable arm of the switch, so as to open the switch and the electrical circuit in which the bimetallic temperature protector is connected.
Other devices, such as the thermal relay shown in U.S. Pat. No. 4,885,560 and the thermo-switch shown in U.S. Pat. No. 4,295,114, disclose a fail-safe system whereby a fusible link is represented by a metal, meltable at a predetermined temperature. Upon melting of the fusible link, a spring-driven member acts to push the switch operating plate to an open position.
Another device used in the prior art to safeguard against the danger of fire and changes to the electrical or electronic component or device and the electrical system or apparatus in or with which such component or device is associated is a separate element in the form of a thermal fuse type member which is added in series by soldering, welding, riveting, crimping or attaching in a separate fuse holder which is temperature sensitive and permanently opens at a predetermined temperature setting.
These fail-safe assemblies add additional problems to electrical or electronic devices or components due to looseness, misalignment and high resistance adding to the difficulty in assembly, increasing the cost of manufacture and providing a less reliable apparatus.
In such prior art fail-safe devices, the absence of sufficient force upon melting of the restraining fail-safe or safeguard element does not assure that the fail-safe mechanism in the circuit breaker, thermal relay, thermo-switch and the like electrical devices will effectively create and maintain an open circuit condition in all situations, particularly those where a significant force is required to open the circuit, as in situations where worn contacts are partially welded together during adverse operating conditions.
Therefore, in one aspect of the present invention, improved fail-safe assemblies for such electrical devices are disclosed, utilizing an impact member, initially held from engagement with the operatively associated coacting contacts by a restraining meltable or fusible material, which impact member serves as a driving force. Upon melting of the restraining meltable or fusible material holding the impact member in the non-active or disengaged position, the impact member is released to engage and to hold the coacting contacts in non-contacting relationship, thereby creating and producing a controlled and certain fail-safe assembly.
It is another aspect of the present invention to provide a fail-safe assembly including a meltable or fusible member for an electronic or electrical component, device, system or apparatus with coacting operatively associated contacts which will effectively guard against the danger of fire and damage to the electronic or electrical component, device, system or apparatus as a result of an electrical current overload or increase of ambient temperature for any reason by assuring, upon melting of the meltable member or fusible link, that there is sufficient force created by the fail-safe system to open and maintain open the coacting contacts.
It is another aspect of the present invention to provide a fail-safe assembly including a meltable or fusible member for an electronic or electrical component, device, system or apparatus with coacting operatively associated contacts which will effectively guard against the danger of fire and damage to the electronic or electrical component, device, system or apparatus as a result of an electrical current overload or increase of ambient temperature for any reason by assuring, on melting of the meltable or fusible member, that there is sufficient force created in the fail-safe system to open and maintain open the coacting contacts so that the dangerous condition will not reoccur.
In another aspect of the present invention to provide a miniature bimetallic circuit breaker which effectively protects components, devices, systems and associated apparatus from damage that could result from overload and unacceptable increases in temperature having, a first current-carrying terminal and a second current-carrying terminal mounted in spaced relation to each other, a snap acting bimetallic actuator connected at one end to said first current-carrying terminal and having a contact at the end remote from the connected end, said second current-carrying terminal having a fixed contact formed thereon, and said movable arm or plate disposed to extend relative said second current-carrying terminal for operative engagement of the contact thereon with the fixed contact on said second current-carrying terminal, and a fail-safe assembly including an impact member disposed for engagement of sand bimetallic actuator, a meltable member normally maintaining the impact member out of engagement with the bimetallic actuator whereby, on melting of the meltable member, the stressed impact member is released with sufficient force to engage and hold the bimetallic actuator in an inoperative position.
It is another object of the present invention to provide an improved fail-safe assembly to guard against the danger of fire and damage in an electrical circuit for an electrical or electronic component, a current-carrying system or associated apparatus with coacting contacts including, an impact member capable of generating high-impact forces, a meltable member for normally maintaining the impact member under stressed conditions wherein on melting of the meltable member, said impact member will have sufficient force to open and maintain open the coacting contacts.
It is another object of the present invention to provide for use in an electrical circuit having a fail-safe assembly for safeguarding an electrical and electronic component, a current-carrying system or an associated apparatus from danger due to fire or other damage with a visual indicator to show when the fail-safe assembly has been actuated.
It is another object of the present invention to provide an electronic or electrical component, a current-carrying system or an associated apparatus with a fail-safe assembly including, an impact member, and a meltable or fusible member for safeguarding coacting operatively associated contacts therein which can be manufactured at a relatively low cost.
It is still another object of the present invention to provide in an electronic or electrical component a current-carrying system or an associated apparatus with a fail-safe assembly including an impact member and a meltable or fusible member for safeguarding coacting operatively associated contacts therein. The meltable or fusible member is sized and shaped as part of the housing or supporting structure which has softening and melting characteristics so that the impact member will be released by the melting action of the meltable or fusible member at a predetermined temperature.